CN113992046A - ISOS type annular alternating current-direct current three-port hexagonal MMC and control method - Google Patents

ISOS type annular alternating current-direct current three-port hexagonal MMC and control method Download PDF

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Publication number
CN113992046A
CN113992046A CN202111203166.XA CN202111203166A CN113992046A CN 113992046 A CN113992046 A CN 113992046A CN 202111203166 A CN202111203166 A CN 202111203166A CN 113992046 A CN113992046 A CN 113992046A
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alternating current
port
voltage
stage
direct current
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刘飞
黄文慧
庄一展
刁晓光
黄艳辉
查晓明
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Wuhan University WHU
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Wuhan University WHU
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/493—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode the static converters being arranged for operation in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

Abstract

The invention relates to the power converter technology, in particular to an ISOS (integrated service system) type annular alternating current-direct current three-port hexagonal MMC (modular multilevel converter) and a control method, wherein the converter comprises a hexagonal structure formed by connecting six bridge arms end to end, each bridge arm comprises n front-stage inversion units, a rear-stage bidirectional active bridge connected with the n front-stage inversion units and 1 inductor connected in series, six vertexes of the hexagonal structure are sequentially R, W, S, U, T and V, and a RST (reverse version) inversion unit is used as a first alternating current port and is connected with an offshore wind farm; the UVW inversion unit is used as a second alternating current port and connected with an alternating current high-power load; and the bidirectional active bridges on the bridge arms are connected in series to serve as third direct current ports and are connected with the medium-voltage distribution network. The converter adopts device multiplexing, reduces the use of switching devices, and can realize bidirectional flow of energy; the offshore wind power is collected and merged into a direct current power distribution network and consumed on site through the control of the front-stage AC/DC conversion and the rear-stage DC/DC conversion, and the power of the three ports is uniformly managed.

Description

ISOS type annular alternating current-direct current three-port hexagonal MMC and control method
Technical Field
The invention belongs to the technical field of power converters, and particularly relates to an ISOS (integrated service system) type annular alternating current-direct current three-port hexagonal MMC and a control method thereof.
Background
In recent years, the energy crisis is becoming more severe, and new energy power generation becomes a priority development target of each country. The new energy resources and the load demand are distributed in a reverse way, and the new energy resources and the load demand need to be transported to a load center through a long distance; the energy density is low, and the land power station occupies a large area; some countries have limited land resources and the development of onshore wind power and photovoltaic power generation tends to be saturated. For countries with abundant coastal resources, the construction of offshore wind power systems has great development prospect.
Offshore wind power collection has three main forms: high voltage alternating current (power frequency) transmission, high voltage direct current transmission and frequency division transmission. HVAC has economic advantages over short distances, FFTS has better technical cost advantages over medium distances, and HVDC has economic advantages over long transmission distances.
Offshore wind power collection is merged into a direct current distribution network and is consumed on site, and a plurality of devices such as AC/AC conversion, DC/DC conversion and the like are needed. An economical multi-port converter can be used in consideration of the equipment utilization and the reduction of the number of power conversion stages. Currently, power electronic devices are developed towards multiple ports, multiple cascades, multiple flow directions and multiple forms of power conversion.
The invention discloses an energy-feed three-port cascaded converter topology with a hexagonal structure and a control method (application publication No. CN109004866A, application date 2018.09.04) applied to the occasions of medium-high voltage dual-motor driving. The structure adopts the phase-shifting transformer, so that the electrical isolation of a power grid is realized; the structure adopts PWM rectification to realize bidirectional flow of energy of three alternating current ports. When the single motor or the double motors are braked, the generated energy can be fed back to the power grid through the bridge arm inversion unit and the PWM rectification unit, and the utilization of regenerated energy is realized. However, the phase-shifting transformer of this structure increases the volume of the device and limits the scenarios of AC/AC conversion.
The invention relates to an alternating current-direct current multi-port hexagonal modular multilevel converter and a control method (application publication No. CN113437891A, application date 2021.09.24) applied to a scene that offshore wind and light are converged and merged into an alternating current power distribution network. The structure comprises six bridge arms, each bridge arm is connected to the offshore photovoltaic by adopting a bidirectional active bridge unit, the output end of the bidirectional active bridge unit is connected with a full-bridge inversion unit, and the output end of the inversion unit is connected with an inductor in series to form one bridge arm. The six bridge arms are connected end to form two AC ports which are respectively connected with offshore wind power and an AC power distribution network. The structure realizes electrical isolation by adding a DC/DC front end and adopting a high-frequency transformer, utilizes module integration of the device and realizes interconnection of a direct current port, a low frequency and a power frequency alternating current port. However, the offshore photovoltaic module is connected in series and boosted and connected with the bidirectional active bridge unit, insulation of the photovoltaic module needs to be considered, and high voltage stress brings difficulty to model selection of unit switching devices and capacitance parameters.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an input-series output-series (ISOS) type annular alternating current/direct current three-port hexagonal module combined multilevel converter (MMC) and a control method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme: an ISOS type annular alternating current-direct current three-port hexagonal module combined multilevel converter comprises an input side offshore wind power plant, an output side alternating current high-power load and a medium-voltage direct current distribution network; the wind power station further comprises a hexagonal structure formed by connecting six bridge arms end to end, each bridge arm comprises n front-stage inversion units, a rear-stage bidirectional active bridge connected with the front-stage inversion units and 1 inductor connected in series, n is a positive integer larger than or equal to 1, six vertexes of the hexagonal structure are R, W, S, U, T, V in sequence, and the RST inversion unit serves as a first alternating current port and is connected with an offshore wind farm; the UVW inversion unit is used as a second alternating current port and connected with an alternating current high-power load; and the bidirectional active bridges on the bridge arms are connected in series to serve as third direct current ports and are connected with the medium-voltage distribution network.
A control method of an ISOS type annular alternating current-direct current three-port hexagonal module combined multilevel converter is characterized in that a preceding stage inversion unit adopts port current dq decoupling control: obtaining a current d-axis instruction of the first alternating current port according to the power balance of the first alternating current port, the second alternating current port and the third direct current port; respectively tracking a dq axis reference value by a PI controller through currents of a first alternating current port and a second alternating current port, introducing an alternating current side voltage feedforward dq axis component and an inductive coupling voltage compensation component, generating voltage modulation waves of the first alternating current port and the second alternating current port to synthesize bridge arm voltage signals, and further obtaining switching signals of an inversion unit; the horizontal phase shift modulation is adopted to realize the phase shift of switching signals of the inversion units among the bridge arms and generate the switching signals of each inversion unit;
the latter two-way active bridge adopts phase shift control: collecting input voltage of each inversion unit, and tracking reference value V of capacitor voltage by PI controllerrefOutputting phase shifting angles of the primary side and the secondary side of the isolation transformer to realize voltage sharing in each inversion unit; and collecting the output voltage of each inversion unit, and outputting a phase shift angle of the secondary side of the isolation transformer between the inversion units by adopting a PI (proportional integral) controller to realize voltage sharing between the inversion units.
Compared with the prior art, the three-port hexagonal module combined multilevel converter is used for merging deep sea low-frequency wind power and offshore photovoltaic into an alternating current power distribution network, and the three-port hexagonal module combined multilevel converter adopts device multiplexing, so that the use of switching devices is reduced, and the bidirectional flow of energy can be realized; the utilization rate of equipment can be improved, and the number of stages of alternating current-direct current power conversion is reduced. The offshore wind power is collected and merged into a direct current power distribution network and consumed on site through the control of the front-stage AC/DC conversion and the rear-stage DC/DC conversion, and the power of the three ports is uniformly managed. The invention is based on a two-port hexagonal MMC, has good low-frequency characteristics, is connected into a frequency division power transmission system and an alternating-current power distribution network, and is additionally provided with a high-frequency boosting isolation circuit connected into near-shore photovoltaic at the front end of each submodule of the MMC, so that the ISOS type annular alternating-current and direct-current three-port hexagonal MMC applied to offshore wind-light alternating-current and direct-current collection is formed. The control method based on the topological structure provided by the invention realizes the control of frequency conversion, voltage transformation and alternating current-direct current conversion, and can meet the requirement of synchronous completion of DC/AC inversion and AC/AC frequency conversion of an alternating current power distribution network for power transmission.
Drawings
Fig. 1 is an embodiment of the invention, which is an topology of an ISOS-type annular ac/dc three-port hexagonal module combined multilevel converter;
FIG. 2 is a mathematical model of an ISOS-type annular AC/DC three-port hexagonal module combined multilevel converter topology according to an embodiment of the present invention;
FIG. 3 is a control block diagram of a preceding stage AC/DC conversion according to one embodiment of the present invention;
FIG. 4 is a control block diagram of a post-stage DC/DC conversion in accordance with one embodiment of the present invention;
FIG. 5(a) is a graph of a voltage waveform at a first AC port in accordance with one embodiment of the present invention;
FIG. 5(b) is a graph of a current waveform at a first AC port in accordance with one embodiment of the present invention;
FIG. 5(c) is a graph of a voltage waveform at a second AC port in accordance with one embodiment of the present invention;
FIG. 5(d) is a current waveform diagram of a second AC port in accordance with one embodiment of the present invention;
FIG. 6 is a graph of capacitor voltage waveforms of submodules between bridge arms according to an embodiment of the present invention;
fig. 7 is a waveform illustrating power distribution among the first ac port, the second ac port, and the third dc port according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.
The deep sea low frequency wind power and offshore photovoltaic are merged into an alternating current distribution network, and two or more independent frequency conversion, voltage transformation and alternating current-direct current conversion devices are usually needed. In order to improve the utilization rate of equipment and reduce the number of alternating current/direct current power conversion stages, this embodiment studies how to use a single power electronic transformer to realize the interconnection of two different frequency alternating current systems and a direct current system. Because the two-port hexagonal MMC topology has good low-frequency characteristics, a frequency division power transmission system and an alternating-current power distribution network are accessed, a high-frequency boosting isolation circuit is added at the front end of each module of the MMC sub-system to access near-shore photovoltaic, and the ISOS type annular alternating-current/direct-current three-port hexagonal MMC applied to offshore wind-light alternating-current/direct-current collection is formed. Meanwhile, a control strategy for realizing frequency conversion, voltage transformation and alternating current-direct current conversion is provided so as to meet the requirement of synchronous completion of DC/AC inversion and AC/AC frequency conversion of an alternating current power distribution network for power transmission.
The embodiment is realized by the following technical scheme that as shown in fig. 1, an input side of the ISOS-type annular alternating current/direct current three-port hexagonal module combined multilevel converter is formed by connecting six bridge arms end to end and presents a hexagonal structure, each bridge arm is formed by connecting n inverter units and 1 inductor in series, and n is a positive integer. The six vertexes are named R, W, S, U, T, V in sequence, RST is a first alternating current port and is connected with an offshore wind farm, and three-phase voltages are vr,vsAnd vtThree phase currents are respectively iu,ivAnd iw. UVW is a second alternating current port and is connected with an alternating current high-power load, and three-phase voltage of the UVW is vu,vvAnd vwThree phase current is iu,ivAnd iw(ii) a The rear-stage DC/DC adopts a bidirectional active bridge, and the output side of the bidirectional active bridge is connected in series and is connected with a medium-voltage direct-current distribution network to form a third direct-current port. The first AC port input transmits energy to the second AC port through the inverter unit for surplusThe energy of the three ports is transmitted to the third direct current port through the inverter unit and the bidirectional active bridge, and the power distribution of the bridge arm is influenced by the power transmission of the three ports.
An equivalent schematic diagram of a hexagonal MMC is shown in fig. 2. Each leg can be equivalent to a series connection of a voltage source and an inductor. Bridge arm voltage is vbiWhere i is 1, …,6 and the bridge arm current is ibi. The neutral point of the first alternating current port is N1The neutral point of the second AC port is N2. Setting the second AC port as a reference point, and setting the offset voltage of the first AC port to be v compared with the neutral point of the second AC portN。
A control method of an ISOS type annular alternating current-direct current three-port hexagonal MMC is disclosed, as shown in figure 3, a preceding-stage AC/DC unit adopts port current dq decoupling control, three-phase voltage signals of two alternating current ports are output, a bridge arm voltage signal is synthesized, and then a unit switch signal is obtained; and horizontal phase shift modulation is adopted to realize the phase shift of the unit switch signals between the bridge arms.
Specifically, the preceding stage AC/DC unit adopts port current dq decoupling control: and obtaining a current d-axis instruction of the first alternating current port according to the power balance of the first alternating current port, the second alternating current port and the third direct current port. And the currents of the first alternating current port and the second alternating current port respectively adopt a PI controller to track the dq axis reference value, and introduce an alternating current side voltage feedforward dq axis component and an inductive coupling voltage compensation component to generate voltage modulation waves of the first alternating current port and the second alternating current port. And considering the characteristics of the converter, in order to optimize the characteristics of ports, horizontal phase shift modulation is adopted to realize the phase shift of signals between bridge arms, and switching signals of each inversion unit are generated.
As shown in fig. 4, the post-stage DC/DC unit adopts phase shift control: collecting input voltage of each module submodule, tracking a capacitor voltage reference value by adopting a PI (proportional integral) controller, and outputting a phase shift angle of an original secondary side to realize voltage sharing in the module; and collecting the output voltage of each module, and outputting the phase shift angle of the secondary side between the modules by adopting a PI controller to realize voltage sharing between the modules.
Specifically, the post-stage DC/DC unit adopts phase shift control: collecting input voltage of each inversion unit, and using PI controller to control the inversion unitTracking capacitor voltage reference value VrefOutputting phase shifting angles of the primary side and the secondary side of the isolation transformer to realize voltage sharing in each inversion unit; and collecting the output voltage of each inversion unit, and outputting the phase shift angle of the secondary side of the isolation transformer between the modules by adopting a PI controller to realize voltage sharing between the inversion units.
The port characteristics are shown in fig. 5(a), 5(b), 5(c), and 5 (d). As can be seen from fig. 5(a) a voltage waveform diagram of the first ac port, fig. 5(b) a current waveform diagram of the first ac port, fig. 5(c) a voltage waveform diagram of the second port, and fig. 5(d) a current waveform diagram of the second ac port, the characteristics of the respective ports are good.
FIG. 6 is a graph of the waveform of the capacitor voltage of the submodule between bridge arms, and the result shows that the direct voltage is stable.
Fig. 7 is an inter-port power distribution, and the results show that three ports are power balanced.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims (2)

1. An ISOS type annular alternating current-direct current three-port hexagonal module combined multilevel converter comprises an input side offshore wind power plant, an output side alternating current high-power load and a medium-voltage direct current distribution network; the method is characterized in that: the wind power station further comprises a hexagonal structure formed by connecting six bridge arms end to end, each bridge arm comprises n front-stage inversion units, a rear-stage bidirectional active bridge connected with the front-stage inversion units and 1 inductor connected in series, n is a positive integer larger than or equal to 1, six vertexes of the hexagonal structure are R, W, S, U, T, V in sequence, and the RST inversion unit serves as a first alternating current port and is connected with an offshore wind farm; the UVW inversion unit is used as a second alternating current port and connected with an alternating current high-power load; and the bidirectional active bridges on the bridge arms are connected in series to serve as third direct current ports and are connected with the medium-voltage distribution network.
2. The control method of the ISOS type annular AC/DC three-port hexagonal module combined multilevel converter according to claim 1, wherein:
the preceding stage inversion unit adopts port current dq decoupling control: obtaining a current d-axis instruction of the first alternating current port according to the power balance of the first alternating current port, the second alternating current port and the third direct current port; respectively tracking a dq axis reference value by a PI controller through currents of a first alternating current port and a second alternating current port, introducing an alternating current side voltage feedforward dq axis component and an inductive coupling voltage compensation component, generating voltage modulation waves of the first alternating current port and the second alternating current port to synthesize bridge arm voltage signals, and further obtaining switching signals of an inversion unit; the horizontal phase shift modulation is adopted to realize the phase shift of switching signals of the inversion units among the bridge arms and generate the switching signals of each inversion unit;
the latter two-way active bridge adopts phase shift control: collecting input voltage of each inversion unit, and tracking reference value V of capacitor voltage by PI controllerrefOutputting phase shifting angles of the primary side and the secondary side of the isolation transformer to realize voltage sharing in each inversion unit; and collecting the output voltage of each inversion unit, and outputting a phase shift angle of the secondary side of the isolation transformer between the inversion units by adopting a PI (proportional integral) controller to realize voltage sharing between the inversion units.
CN202111203166.XA 2021-10-15 2021-10-15 ISOS type annular alternating current-direct current three-port hexagonal MMC and control method Pending CN113992046A (en)

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